Study On The Blending Ratio Measurement Of Biomass And Coal Co-firing By ¹⁴C Method

The technology of biomass and coal co-firing has advantages,such as replacing coal fuel and reducing carbon dioxide emission.However,the reliable biomass identification technology is absent to support subsidy policy,which concentrates most of the biomass resources to biomass direct fired boilers in China.¹⁴C is a radioactive carbon isotope with a half-life of 5730 years.At present,the atomic ratio of ¹⁴C/12 C in the atmosphere is about 1.2×10-12.14 C in fresh biomass remains the same level as that in the atmosphere,while 14 C in fossil fuels such as coal was zero through million years decay under the ground.14 C method is able to measuring the blending ratio of co-firing boilers by measuring 14 C activity of flue gas.In order to promote the industrial application of co-firing power generation technology in China,this study proposes a reliable measurement method of biomass blending proportion based on 14 C method.This industrial measuring method is studied in detail,and its feasibility is verified by experiments.The accuracy of ¹⁴C activity test is the basis of 14 C method.In this study,LSC benzene synthesis and AMS graphitization are selected as the 14 C testing technology.In order to understand the basic theory of sample preparation and on-line test,and accumulate research experience,high vacuum benzene synthesis system and multifunctional graphitization system are built.And the corresponding standard flow is developed.Comparing the two technical routes,it is found that AMS graphitization method has higher precision and lower time cost and labor cost for sample preparation and test,but the instrument cost and test cost is more than 10 times of LSC benzene synthesis.Meanwhile,considering the limitations of the existing 14 C testing technology,this study proposes and explore preliminarily two new technical routes of 14 C test,AMS positive pressure graphitization and LSC liquid phase/supercritical CO2,which can measure 14 C activity of flue gas more quickly.Then,this study simulates the fuel combusting and flue gas capturing of the industrial field.Two kinds of biomass pine sawdust and corn straw,and three kinds of coal,Changzhi anthracite,Shenmu bituminous coal and Zhundong lignite are co-fired on a continuous feed drop-tube furnace.The co-combustion flue gas is collected for14 C activity testing.Under the ideal condition of laboratory,the measurement results of the two 14 C test routes both reflect the actual blending ratio accurately.When the carbon based biomass blending ratio is within the range of 1 %-11 %,the deviation between 14 C method measuring results are less than 0.5 % from the actual value of biomass blending ratio.AMS graphitization method has good measurement accuracy.Its absolute error of 95 % confidence interval is ± 0.09 %.Although the maximum error of LSC benzene synthesis method reaches ± 0.55 %,its absolute error decreases obviously with the decrease of biomass blending ratio.Moreover,the linear fitting of the 14 C method measuring results shows that the LSC benzene synthesis method has a good linearity（R2 = 0.997）and accuracy.However,in the actual industrial scenario,the system error caused by the air CO2 pollution and the inaccurate reference value of biomass fuel 14 C activity should be considered.In order to update the prediction theory of biomass reference 14 C activity,this study carry out field sampling and testing in Guigang and Suqian,and compare the results with relevant literature.The results showed that time,fossil carbon emission and plant species are the main factors that determine the 14 C activity of plants.This study proposes a reasonable empirical formula for the prediction of 14 C activity reference value of biomass fuel.For air CO2 pollution,although the air entering the flue gas due to combustion oxygen supply is ineluctable,it can be deducted from the calculation based on the air CO2 concentration and¹⁴C activity in the power plant.At the same time,the CO2 in the flue gas can be quickly converted into carbonate or other state hard to pollute for preservation to control the proportion of air CO2 in the sample less than 0.50 %.Based on the experimental results of the settling furnace,the measurement error range of 14 C method applied to the actual industrial scenario is calculated reasonably.The maximum error of LSC benzene synthesis method increased to ± 0.81 %,which is still within the acceptable range of industrial test.But the maximum error of AMS graphitization method is also increased to ± 0.57 %,which almost waste the high precision of this 14 C testing technology.Finally,a complete industrial test scheme of 14 C method is given,which is suitable for both direct and indirect biomass co-firing.And it is brought into the industrial site of a biomass biochemical coupled pulverized coal boiler in Hubei Province.The 14 C industrial test scheme accurately measured the 2 %-3 % biomass energy base blending ratio in the industrial site.At present,there are many projects of biomass gasification coupled pulverized coal boiler in operation or in plan in China.The industrial test scheme of 14 C method has a good industrial application prospect.